Welding question - how to weld mild steel to stainless?

Paladin · December 17, 2007, 02:57:51 PM

I'm finally getting around to trying to repair the rusted cross members above my luggage bays.

Reference thread: http://www.busconversions.com/bbs/index.php?topic=6278.msg59817#msg59817

Does anyone have any tips and suggestions for mig welding to the stainless? Positive polarity and stainless wire I assume?
Anything else?
I don't have a trimix gas, only argon. I'm a beginner welder so any hints are appreciated.

Thanks!!

-Dave

kyle4501 · December 17, 2007, 03:10:15 PM

Go to your local welder supply store. They should be able to fix you up.

If I remember correctly, you'll want to use ss-309 wire to weld carbon to ss-304.

CRS prevents me from knowing what gas to use. . . .

jackhartjr · December 17, 2007, 03:20:06 PM

Kyle, funny you said that...when I stole, (Bought) my welder off e-bay he gave me about 40 pounds of mostly SS welding sticks!
Jack

Kristinsgrandpa · December 17, 2007, 04:02:59 PM

I have certified to weld 3 times in my life as a construction worker but none of them were with stainless.

That said, I'll tell you what a pipefitter welder told me. The number on the welding wire/rod is supposed to be higher numerically than the material you are welding. That means Kyle gave you good advise. Also the 309 and 315 rods are made specifically for welding stainless to mild steel. If your steel is 304 then the 309 should work well.

Now I'll tell you something from experience, as I've used over 150 lb of stainless rods, on carbon steel, at home on projects and have found out that using other than 309 or 315 rods the welds will crack sometimes, depending on the thickness of the material being welded. The thicker the steel the more prone to cracking.

Now the answer to this problem is to leave a slight gap between the two metals to allow for shrinkage as the weld cools.

All of my experience with stainless has been with stick welders.
I have two mig welders right now and have never used either for stainless.

Stainless rods work/weld beautiful with AC or DC welders.

One of my migs is set up to weld gas or flux core and I use C-25 (75% argon 25% CO2) but dont know how it works on stainless.

I use the C-25 exclusively for tig also, and it works good on stainless.

Kyle was right again about asking the welding supply man about the right wire and gas. He'll know, and wont tell you wrong, he's there to help and get you to come back.
Ed

Chaz · December 17, 2007, 04:16:46 PM

MIG-ing stainless is the same as mild. You just have to use the correct wire and a Tri-mix shielding gas. You can do it with argon/Co2 but it doesn't do a very good job. You need a little helium in with it for the weld to flow right.
A welding supplier can help you out.
Chaz

boogiethecat · December 17, 2007, 05:50:38 PM

ACTUALLY
Nothing special needs be done when welding mild steel and stainless together. Just use your mig welder and the same old standard steel welding wire (ER70S6) that you'd use with mild steel. And no special gas is needed either... mig mix or plain old CO2 is fine. I only use CO2.

The deal is, all stainless contains iron just like steel does, but also it contains nickel chrome and a few other metals. When you weld mild steel to stainless what you'll get if you use ER70S6 wire is a gradient of alloys from one side of the weld to the other.. the bead will be mostly stainless right where the weld joins to the stainless piece, an alloy mixture of stainless and mild steel (mostly mild steel) within the weld melt itself, and mild steel at the other side. IF you use stainless steel wire, it will be the opposite... stainless where it joins to the stainless part, mostly stainless within the bead itself, and transitioning to mild steel where the bead connects to the mild steel side. The weld in either case will take on (mostly) the characteristics of the welding wire. Stress cracking is really not an issue if you use ER70S6 wire... if you use a more brittle or hard wire then it could be a problem. But the weld will take on the mechanical characteristics of the welding wire for the most part, and ER70S6 is fine for almost everything you'll do on a bus.

I've welded lots of stainless to mild steel and if corrosion resistance isn't a worry (how could it be in this case?) then simple ER70S6 and NO extra hassles is all it takes to make great welds.
That said I wouldn't try it with a stick welder.. only a mig...

Cheers
Gary

frank-id · December 17, 2007, 06:02:58 PM

There are several stick electrodes for welding stainless to mild steel. About a dollar per stick at 1/8 X 14 inches. Frank in Idaho

gumpy · December 17, 2007, 08:18:28 PM

I did what Gary said. Used standard steel wire and Argon/CO2 mix. Replaced all the side framing on my MC9 this way w/ bracing. Haven't had a problem with it. Can't see any of the welds any longer as they've been covered on the interior, but I ran the bus for a couple years before getting the interior walls in, and there was no indication of problems.

JohnEd · December 18, 2007, 12:46:25 AM

Gary,

Al of my welding "How to's" said to use argon/ co2 75% to 25%. They weren't wisy washy about that. Yopu and a couple of welding shops i trust seriously use 100% co2. One told me that co2 will give a "stronger" but less pretty weld but the mix was easier to use and, as said, better looking welds. Why do you prefer 100% co2?

Using mild steel wire seems the logical move unless there is a technical reason against it. If it were more difficult to get a "safe" weld i sure would opt for another wire and gas.

Two years without a problem? Isn't that called PROOF?

Thanks, Gary

John

JackConrad · December 18, 2007, 05:00:38 AM

I use standard mild steel wire and CO2/Argon gas mix. The guy at the welding supply shop said it would work just as good as the SS wire except the mild steel wire cannot be polished to match the SS and will probably get a layer of rust on the surface of it. Jack

Chris 85 RTS · December 18, 2007, 07:17:59 AM

I think the real question here is is what you are welding considered structural and thus your life will depend on it?

If no, then I agree with Gary and have done the same myself. In fact, I have found it welds really nice. It is technically correct, probably not, but a crack in the bracing for my entry steps is not going to bring the space shuttle down.

If yes, then I would pay a professional to weld it up for you. Why risk your life or others to save a few bucks?

boogiethecat · December 18, 2007, 10:40:55 AM

John,
It's pretty simple, any of the gasses will work fine and it is true that the argon mixes or pure argon will be easier to use (not by much though) and less messy. "Messy" simply meaning that CO2 creates a lot of splatter balls which you will probably want to scrape off when you're done. "Easier welding with a mix" is mostly due to the slightly improved smoothness of the weld bead and less splattering as you go. For me though, mixes are not worth it unless I'm welding 1/2" stuff with a 300 amp welder, which isn't frequently, and in which case I use pure argon simply because I have it around for my stainless and aluminum work.

I got on to using pure CO2 when probably the best welding guy I've ever known (certified and experienced in everything from mine work to aerospace turbines) told me "try it, you'll like it". He was right. It's structurally just as good as anything else, and the big plus is how long the tanks last (and cost to refill). With a given sized tank and amount of monthly welding, an argon mix tank ($75 to refill) lasts me maybe a month. The same size tank of CO2 ($40 to refill) will go almost a year. That in itself, with the amount of steel I weld, is the deal maker. It's because CO2 comes as a compressed liquid whereas the mixes are compressed gases. MANY more molecules in a given space with a liquid!!! No wonder the local shop wants to sell you mix- they get more of your wallet every time you show up!!

Chris- in answer to "is what you are welding considered structural and thus your life will depend on it?" I strongly believe that the talent and experience of the guy doing the welding is absolutely important in this matter, and fairly unimportant is what welding gas he uses. The way I look at it, everything I weld on my bus can be considered "life will depend on it", from the overhead racks that hang over my driver's seat to the Telma retarder brackets I made, and from the rails that hold my poo tanks from falling on the street as I drive, to the brackets holding my genset to the bus frame.
I would venture to state that until someone learns to weld *properly*, he should not be welding ANYTHING on a bus. Fortunately it's not difficult to learn what is a good weld and what isn't, and even easier with todays Mig technology to learn to do good welds even if you're not a seasoned welding guy.

The learning process can be had by welding a lot of scrap pieces together, or taking lessons. Both is better! I like the idea of having an experienced welder help you out at first, because there are many things about it that you can't get from a book (like how making a good weld SOUNDS) and it's easy to pick up when you're shown. One BIG thing when learning to use a mig is to have someone turn the wire-feed speed and current knobs WHILE you're doing a long even weld. That way you get an instant grokk on what these settings do and it's really obvious when it's right. That one is hard to learn on your own because you can't be doing a continuous weld and turning the knobs to see what happens as you go...

Here's a couple of photos that I thought you'd all like... first one is my Crown as I raised the roof, with my trusty Miller blue.
Second one is the inert gas welding chamber that I put together (took me a few years getting all the parts from ebay), which I use to weld any stainless steel things that will go inside of it! It's amazing to weld stainless in a totally inert atmosphere... like playing with puddles of mercury...

JohnEd · December 18, 2007, 08:39:42 PM

El Boggie,

Thank you. I am now a CO2 guy. If small spatters are the only issue I can handle that. Thought there was more of an issue but am glad to know there isn't and I have that option.

Do you have more pics of your Crown? What engine and HP? Tx?

Thanks again,

John

boogiethecat · December 19, 2007, 09:26:00 AM

JohnEd · December 19, 2007, 10:05:50 PM

Gary,

That is INCREDIBLE! What a trip. People like you made this country. I looked at every pic at least twice.

What part of SD? I lived there and your spread looks more like Escondido suburbs.

Thanks,

John